Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $208.33   8.832%   $226.7297   $226.73   $226.75   $226.70  
  Purchase #2 $26.71   7.423%   $28.6927   $28.69   $28.70   $28.70  
  Purchase #3 $130.55   11.208%   $145.182   $145.18   $145.20   $145.20  
  Purchase #4 $238.48   12.367%   $267.9728   $267.97   $267.95   $268.00  
  Purchase #5 $69.65   10.672%   $77.083   $77.08   $77.10   $77.10  
  Purchase #6 $90.91   4.359%   $94.8728   $94.87   $94.85   $94.90  
  Purchase #7 $174.48   6.596%   $185.9887   $185.99   $186.00   $186.00  
  7 purchase totals = $939.11       $1,026.5217   $1,026.51   $1,026.55   $1,026.60